Backup slides
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
CMS as a Detector for CMS as a Detector for
Heavy Ion Physics Heavy Ion Physics Silicon Tracker
• Good efficiency and low fake rate for pT>1 GeV
• Excellent momentum resolution Dp/p~1%
Fine Grained High Resolution Calorimeter (E-cal+H-cal)
• Hermetic coverage up to |h|<5
• (|h|<7 proposed using CASTOR)
• Zero Degree Calorimeter (proposed)
Muon Reconstruction
• Tracking m from Z0, J/ψ, ϒ
• Wide rapidity range |h|<2.4
• σm ~50 MeV at ϒ
• Zero Degree Calorimeter (proposed)
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
CMS as a Detector for CMS as a Detector for
Heavy Ion Physics Heavy Ion Physics
Si Tracker including Pixels
Silicon Tracker
• Good efficiency and low fake rate for pT>1 GeV
• Excellent momentum resolution Dp/p~1%
Fine Grained High Resolution Calorimeter (E-cal+H-cal)
• Hermetic coverage up to |h|<5
• (|h|<7 proposed using CASTOR)
• Zero Degree Calorimeter (proposed)
Muon Reconstruction
• Tracking m from Z0, J/ψ, ϒ
• Wide rapidity range |h|<2.4
• σm ~50 MeV at ϒ
• Zero Degree Calorimeter (proposed)
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
CMS as a Detector for CMS as a Detector for
Heavy Ion Physics Heavy Ion Physics
Si Tracker including Pixels ECAL
HCAL
Silicon Tracker
• Good efficiency and low fake rate for pT>1 GeV
• Excellent momentum resolution Dp/p~1%
Fine Grained High Resolution Calorimeter (E-cal+H-cal)
• Hermetic coverage up to |h|<5
• (|h|<7 proposed using CASTOR)
• Zero Degree Calorimeter (proposed)
Muon Reconstruction
• Tracking m from Z0, J/ψ, ϒ
• Wide rapidity range |h|<2.4
• σm ~50 MeV at ϒ
• Zero Degree Calorimeter (proposed)
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
CMS as a Detector for CMS as a Detector for
Heavy Ion Physics Heavy Ion Physics
Si Tracker
• Good efficiency and low fake rate for pT>1 GeV
• Excellent momentum resolution Dp/p~1%
Fine Grained High Resolution Calorimeter (E-cal+H-cal)
• Hermetic coverage up to |h|<5
• (|h|<7 proposed using CASTOR)
• Zero Degree Calorimeter (proposed)
Muon Reconstruction
• Tracking m from Z0, J/ψ, ϒ
• Wide rapidity range |h|<2.4
• σm ~50 MeV at ϒ
• Zero Degree Calorimeter (proposed)
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
CMS as a Detector for CMS as a Detector for
Heavy Ion Physics Heavy Ion Physics
Si Tracker including Pixels ECAL
HCAL
µµµµ chambers
Fully functional at highest expected multiplicities
Detailed studies at dN/dy~3000-5000 and cross-checks at 7000-8000
Silicon Tracker
• Good efficiency and low fake rate for pT>1 GeV
• Excellent momentum resolution Dp/p~1%
Fine Grained High Resolution Calorimeter (E-cal+H-cal)
• Hermetic coverage up to |h|<5
• (|h|<7 proposed using CASTOR)
• Zero Degree Calorimeter (proposed)
Muon Reconstruction
• Tracking m from Z0, J/ψ, ϒ
• Wide rapidity range |h|<2.4
• σm ~50 MeV at ϒ
• Zero Degree Calorimeter (proposed)
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
CMS as a Detector for CMS as a Detector for
Heavy Ion Physics Heavy Ion Physics
Si Tracker including Pixels ECAL
HCAL
µµµµ chambers
Fully functional at highest expected multiplicities
Detailed studies at dN/dy~3000-5000 and cross-checks at 7000-8000
DAQ and Trigger
High rate capability for AA, pA, pp High-Level Trigger capable of
inspecting/selecting HI events in real-time
Silicon Tracker
• Good efficiency and low fake rate for pT>1 GeV
• Excellent momentum resolution Dp/p~1%
Fine Grained High Resolution Calorimeter (E-cal+H-cal)
• Hermetic coverage up to |h|<5
• (|h|<7 proposed using CASTOR)
• Zero Degree Calorimeter (proposed)
Muon Reconstruction
• Tracking m from Z0, J/ψ, ϒ
• Wide rapidity range |h|<2.4
• σm ~50 MeV at ϒ
• Zero Degree Calorimeter (proposed)
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
The Objective The Objective Reconstruct Primary charged particles Cover wide range in pT ~1 GeV and up
Need coverage in 2π and –2.5<eta<2.5, as hermetic as possible
Need robust algorithms to work in a high track density environment
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
The Algorithm The Algorithm
Adapted from default p+p reconstruction.
Based on Kalman Filter
Modifications to the p+p Algorithm:
Trajectory Seed Generation
Three pixel hit combinations compatible with primary event vertex Trajectory Building
Special error assignment to merged hits Trajectory cleaning
Allow only one track per trajectory seed Trajectory Smoothing
Final fit with split stereo layers
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
Geometrical Acceptance Geometrical Acceptance
• Track cross more than 8 (~12 hits) detector layers and hits in
three pixel layers.
• Geometrical acceptance ~80%
• Defines cutoff at low pT (~1GeV)
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
B tagging a jet B tagging a jet
A jet from a b quark has a secondary vertex typically a few mm from the primary, and therefore tracks with large impact parameters In HLT the direction of the jet is given by the calorimeter
The size of the tracking region is defined by the properties of B-jets Partial reconstruction is defined by limiting the number of hits
– Impact parameters expensive to check during track building
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
Tracker use in jets Tracker use in jets
In addition to B tagging, the tracker can improve
– Jet energy measurement – Jet direction estimate
– Separate jets from trigger and pile-up events
All this comes at a (CPU) price. So no matter how fast the track reconstruction, it will never be fast enough (some even consider global reconstruction of all tracks at
HLT to improve missing Et resolution)
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
0-0,7 1,2-1,6 1,6-2,0 2,0-2,4
ηηηη Range
Et=100 GeV ∆R<0.4 No-Pileup
Track Efficiency (for b tracks) (5 hits)
Fake Rate (5 hits)
Fake Rate below 1%
Track Reconstruction ~ 150
Track Reconstruction ~ 150--200 200 msecmsec CPU@1GHzCPU@1GHz
Tracker could be used @ HLT on complex events Tracker could be used @ HLT on complex events
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
Pixel Triplet Seeds Pixel Triplet Seeds
• Pixel triplets provide precise initial estimate of momentum components.
• Generate only seeds by consistent with primary event vertex (constraint: δr 100mm δz 350mm)
• Minimal number of seeds is crucial for runtime performance and low number of fake tracks
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
Pixel Reconstruction
Pixel Reconstruction –– Track ParametersTrack Parameters
Pixel detector provides good pT resolution for low energetic tracks. Poor pT assignment
for particle above 10 GeV.
The impact parameters
resolutions degrades for low pT tracks. Small Transverse I.P. resolution dependence vs pseudorapidity. Important
dependency for longitudinal I.P.
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
Tracker Alignment Tracker Alignment
Some tools for Alignment studies available
9--14 June 200514 June 2005 Tracking at LHC L. Silvestris
Alignment: Placement accuracy and reproducibility Alignment: Placement accuracy and reproducibility
with automatic pattern recognition with automatic pattern recognition
Image found: place Image found: place Sensor pair precisely Sensor pair precisely
“Gantry see, Gantry do”
The gantry system localizes automatically the components to be assembled by
searching for a Marker with a camera
σ∆Φ∆Φ∆Φ∆Φ
30 µµµµrad
σ∆∆∆∆X 3 µµµµm
Sensors within a module are
placed to better than 5µ and 0.1mrad Relative to each other
Mis-placements of up to 10µ do not significantly degrade the
Ultimate muon Pt resolution even if not corrected for
in track reconstruction